The manufacture of cigarette filters from a continuous, multifilament filter tow generally involves processing steps which include separation of the individual filaments (i.e., "opening up" of the tow), the application of plasticizer or other additives to the filter tow and the formation of a continuous filter rod from the treated filter tow. The uniformity and filtering characteristics of the resulting filter rod are largely determined by the effectiveness of these tow processing steps. Thus, there is a substantial amount of prior art which is directed to methods and apparatus for transforming filter tow into cigarette filters having predictable smoke filtration characteristics.
One of the presently used commercial processes for transforming a continuous, multifilament filter tow into a filter rod involves passing the tow through a jet device where the tow is subjected to a high velocity stream of gaseous fluid. The jet device serves to separate the individual filaments from each other and to create a bloomed, substantially round, rope-like appearance in the filter tow as it emerges from the jet device. The bloomed filter tow is then conveyed via delivery rolls to filter rod-forming means where the bloomed tow is compacted into an essentially round filter rod. A typical jet device and processing arrangement is disclosed in U.S. Pat. No. 3,297,506. A disadvantage of this prior art arrangement, however, is that the delivery rolls which convey the filter tow from the jet device to the rod-forming means (i.e., the cigaretting machine) compresses the tow between the opposing surfaces of the delivery rolls thereby causing the tow to assume a flat band configuration. In other words the delivery rolls tend to destroy the advantageous configuration of the bloomed filter tow as it emerges from the jet device. This problem is apparently appreciated by the inventors named in U.S. Pat. No. 3,297,506 in that the use of a stuffer jet at the entrance to the cigaretting machine is disclosed. The stuffer jet restores to some extent the substantially round, rope-like configuration of the filter tow existing at the time it emerges from the blooming jet device. The use of a stuffer jet, however, adds to the processing costs because a pressurized supply of gaseous fluid must be provided for operating the jet. The processing arrangement shown in the above-identified patent as practiced commercially has not, in fact, employed a stuffer jet but, rather, a condensing horn positioned at the entrance to the cigaretting machine.
The prior art appreciates the desirability of forming a filter rod from tow that has been shaped into a rope-like configuration by an air jet rather than by gathering and compacting from a thin flat band of tow. Thus, column 6 (lines 7-18) of U.S. Pat. No. 3,411,942 teaches that less liquid additive (e.g., plasticizer) will be coated on the delivery rolls and less folding and crumpling of the tow will be realized if the tow is conveyed to the filter rod-forming means in a cylindrical shape. In spite of the recognition that formation of a filter rod from a flat band of tow is less desirable than formation from a rope-like configuration, this patent fails to teach an alternative to the delivery roll arrangement which compresses the filter tow between the opposing surfaces of the rolls.